Americans are more concerned about the changing planet when the words "global warming" are used than when they hear "climate change," new research finds.

The two terms are often used synonymously, but new surveys reveal that they carry different connotations for many people, particularly African Americans, Hispanic Americans, liberals and people between the ages of 31 and 48. Republicans see the two terms as more or less equivalent, but Democrats, political independents, liberals and moderates are more likely to express concern about "global warming" than "climate change."

"The studies found that the two terms are often not synonymous — they mean different things to different people — and activate different sets of beliefs, feelings and behaviors, as well as different degrees of urgency about the need to respond," the researchers wrote in a report released on May 27. [8 Ways Global Warming Is Already Changing the World]

A history of two terms

The term "climate change" is about 20 years older than the term "global warming." Wallace Broecker, a geoscientist at Columbia University known as the "Grandfather of Climate Science," coined the latter term in 1975. Even for scientists, the two terms have different definitions.

"Global warming refers to the increase in the Earth's average surface temperature since the Industrial Revolution, primarily due to the emission of greenhouse gases from the burning of fossil fuels and land-use change," Yale University researcher Anthony Leiserowitz and colleagues wrote in the new report, "whereas climate change refers to the long-term change of the Earth's climate, including changes in temperature, precipitation and wind patterns over a period of several decades or longer."

Many media outlets use the terms interchangeably, and both terms have become politicized. In 2002, Republican strategist Frank Luntz suggested that the George W. Bush administration use the words "climate change" rather than "global warming," because climate change seemed less emotional, and more controllable. Now, however, conservatives tend to use the words "global warming" more, while liberals prefer "climate change," according to a 2011 analysis published in the journal Public Opinion Quarterly.

Google Trends reveals that, historically, Internet users have searched more for "global warming" than "climate change," but the gap has closed in the past couple of years.

Warming or change?

Leiserowitz, who heads the Yale Project on Climate Change Communication, and his colleagues commissioned two national surveys to find out how Americans respond to each term today. One of the surveys, conducted in January, was based on a nationally representative sample of 1,021 adults. The other, conducted in November and December 2013, was based on a nationally representative sample of 1,657 adults.

In the January survey, the researchers asked participants about their experiences with the terms "global warming" and "climate change." They found that Americans reported equal familiarity with both terms but were more likely to use and hear the words "global warming." Forty-five percent reported hearing "global warming" more often, compared with 12 percent who said they heard "climate change" more. (Meanwhile, 37 percent said they heard both terms equally.) And 35 percent of Americans said they used "global warming" more themselves, compared with 16 percent who said they used "climate change" more.

In the November/December survey, the researchers asked participants about their concerns and feelings about climate change. For half of the participants, the questions referred to "climate change." For the other half, the researchers asked the same questions, but with the words "global warming" instead of "climate change."

Overall, the results were striking: Americans were generally more concerned, threatened and moved to act when they were responding to the term "global warming" versus "climate change." For example, respondents were 13 percentage points more likely to say "global warming" is bad than they were to say "climate change" is bad — 76 percent compared to 63 percent.

When participants were asked to free-associate with both terms, "global warming" resulted in more associations with melting ice, flooding and the ozone hole (a different problem). "Climate change" was more closely linked with weather phenomena such as storms. However, "global warming" was more likely to bring up thoughts of severe weather than "climate change."

Sixty-two percent of Americans responded that "global warming" is happening, and 63 percent said that "climate change" is happening. But people feel more certainty about "global warming," the survey found: 27 percent of Americans feel "extremely sure" that "global warming" is happening. When the term "climate change" was used, only 20 percent said they felt that level of certainty. [The Reality of Climate Change: 10 Myths Busted]

Some of these differences are even more extreme when subgroups are considered. For example, men are 12 percent more likely to believe that "global warming" is happening versus "climate change." People between the ages of 31 and 48 are 21 percent more likely to believe in global warming over climate change. And self-described political liberals are 19 percent more likely to feel that extreme certainty when the term "global warming" is used compared with "climate change."

Equal numbers of Americans blame human activities for the changes, no matter which term is used. They're also equally likely to say that scientists agree the world is warming, whether the changes are dubbed "global warming" or "climate change," though liberals and political independents see more scientific consensus when the term "global warming" is used.

The findings suggest that, politically, scientists will gain little by using the term "climate change," as Republicans are equally skeptical of both terms, the researchers conclude. But using "climate change" appears to reduce concern and interest among people on the rest of the political spectrum.

The connotations of the terms could change over time, the researchers warned, but advocates for reducing the problem should know what reactions their language is likely to trigger.

"Scientists often prefer the term 'climate change' for technical reasons, but should be aware that the two terms generate different interpretations among the general public and specific subgroups," the researchers wrote.